Deep rock mass engineering is in high water pressure and high stress environment，its response characteristics are significantly influenced by the environmental conditions，which is an important basis for deep rock mass engineering blasting design and construction. In order to investigate the dynamic response characteristics of the rock under deep high water pressure environment，impact tests were carried out on red sandstone based on a self-developed high water pressure and high stress rock dynamic testing system，and 4 axial static stresses and 9 water pressure levels were set to simulate the occurrence environment of engineering rock mass. The effects of water pressure and axial static stress on the dynamic stress-strain curve and dynamic peak stress of rock were investigated by calculating dynamic stress and strain data of rock based on incident，reflected and transmitted waves. The pre-peak and post-peak energy conversion characteristics of stress-strain curves were considered comprehensively，and the water-inrush tendency index of rocks was defined by energy evolution parameters. The relationships between rock dynamic residual stress，residual strain，water inrush tendency index and wave impedance with water pressure were analyzed，the empirical models of dynamic peak stress strengthening coefficient，residual stress，residual strain，water inrush tendency index，wave impedance and water pressure，as well as dynamic peak stress and axial static stress were constructed. The influence mechanisms of high water pressure and high stress on the dynamic strength and deformation characteristics of rock were explored. The results show that the dynamic stress-strain curves of rock gradually change from type I to type II with the rise of water pressure. Under the same axial static stress，the dynamic peak stress strengthening coefficient，residual stress and wave impedance of the rock increase rapidly at first and then slowly with increasing water pressure，and the water inrush tendency index and residual strain decrease with the increase of water pressure. Under the same water pressure，the peak dynamic stress of the rock decreases as the axial static stress increases. High-pressure water has dual effects on rock dynamic strength，that is，the water wedge effect promotes crack propagation and reduces rock strength，while the Stefan effect and other viscous effects and external confining water hinder the destruction of pore structure and enhance the dynamic strength. The two effects play a game with each other and jointly affect the dynamic response characteristics of rock under deep high water pressure environment. The results of the study are favorable for blasting and excavation of engineering rock mass and stability analysis of surrounding rock under deep high water pressure environment.

Since the Wudongde reservoir area is located in the dry-hot valley area，the rock mass in the hydro-fluctuation zone is in the heat and wet cycle state.  In order to study the damage evolution mechanism of sandstone joints under the action of the heat and wet cycle，the heat and wet cycles and repeated shear tests were designed and conducted on sandstone joints to analyze the shear resistance，the joint surface morphology characteristics，and the evolution law of energy parameters. The research results indicate that：(1) within 12 heat and wet cycles，the shear mechanical parameters and dimensional morphology parameters of sandstone joint surfaces show a degradation pattern of first rapid decrease and then slow stabilization. Among them，the degradation amplitude of each parameter in the first 3 cycles is significantly larger，and then the degradation trend gradually slows down，and tends to stabilize after 8 cycles. (2) As the heat and wet cycle increases，the total energy and dissipated energy of sandstone joints gradually decrease during the shear process，and their changing trend is consistent with the mechanical parameters. In comparison，the change in elastic energy is relatively small，and the trend in dissipated energy is obvious. (3) The shear performance damage mechanism of sandstone joints under the heat and wet cycle includes three aspects. Firstly，the damage effect of the heat and wet cycle on rock wall strength and joint surface morphology. Secondly，the change of joint surface morphology caused by repeated shear and the damage effect of rock mass within a certain depth range of rock wall. Thirdly，the mutual promotion effect of the heat and wet cycle and repeated shear sequence on joint surface damage. The relevant methods and results can provide a good reference for the heat and wet cycle damage degradation analysis of rock joints in the dry-hot hydro-fluctuation zone of the reservoir bank slope.

Water inrush from the mine floor is a significant hazard affecting the safe production of deep coal mines. To investigate the complex phenomenon of water inrush from deep mine floors，the characteristics of water inrush incidents in the working faces of the North China region were examined and analyzed. It is found that most water inrush accidents are caused by the combined effects of disturbance stress and water pressure fluid-solid coupling，leading to floor failure. Under certain mining conditions，a dynamic water hammer effect can form in the fracture rock mass channels of the deep mine floor. This effect causes varying degrees of damage or destruction to the surrounding rock of the mining area，which we define as the water hammer water inrush effect. The essence of the water hammer effect in deep rock masses is the instantaneous interruption of water flow in the fracture channels，causing the water to repeatedly cycle and impact within the channel. This repeated cycling leads to damage to the surrounding rock of the fracture channel. When the energy of the repeatedly cycling water accumulates to a certain state，it causes the fracture to expand and break，resulting in a water inrush disaster. Based on this concept，a progressive-lifting mechanical model of deep mine floor water under the influence of water hammer is established， revealing that the water hammer effect in fracture rock masses may promote the formation of water inrush channels. Theoretical and numerical study results collectively indicate that the faster the water flow in the fracture rock mass channels，the greater the instantaneous pressure formed by the water hammer. Under the influence of the water hammer effect，the water wedge effect further drives the progressive-lifting failure of rock mass fractures. Finally，we categorized the types of water inrush from the mine floor under the influence of water hammer into：water hammer-water wedge-induced water inrush from fracture rock masses，stress erosion-fault-induced water inrush from concealed faults，and water inrush from major structural fault conduits. We also proposed control measures for water inrush from deep mine floors affected by water hammer. The water hammer water inrush effect is a new mechanism proposed for water inrush from mine floors，currently in the preliminary discussion stage，aimed at providing some guidance for understanding and controlling deep mine floor water inrush mechanisms.

To deeply investigate the shear mechanical behaviors and failure mechanisms of rock in the complex engineering environment，a bidirectional dynamic rock shearing test system was independently designed and developed. The test system is mainly composed of five parts：host loading system，servo oil source system，servo control system，shear tooling system and deformation measurement system. The main innovations of the test system are as follows：(1) Dynamic loading can be carried out in the normal and shear directions at a frequency of 0.001–10 Hz，and the mixed loading and unloading control of tangential displacement，tangential load，normal displacement and normal load can be realized simultaneously. The normal center of the sample can be kept constant by the method of bidirectional shear. (2) Load，cylinder displacement，and deformation sensors are used for multi-rate and multi-objective combination control to achieve tangential and normal dynamic and static loading in the test process；(3) Multiple controllable boundary conditions such as constant stress，constant displacement，constant stiffness，dynamic loading and customized load forms can be realized；(4) Large-size specimens with L×W×H = 200 mm×100 mm×100 mm or 400 mm×200 mm×200 mm can be researched；(5) The coupling mechanism under various working conditions such as shearing and anchoring can be explored simultaneously. The reliability and accuracy of the test system were verified by carrying out rock shear tests under different stress boundary conditions with this test system. The test results indicate that the developed bidirectional rock joints dynamic shear test system can meet the scientific research needs of rock shear mechanical behavior. The system is easy to operate and the test process is efficient and stable. The loading accuracy and test data accuracy are high. The test system can provide an important platform for research in major engineering fields such as deep coal resource mining，roadway(tunnel) excavation and construction，radioactive nuclear waste disposal，slope stability analysis in earthquake zones and underground energy storage.

There are issues with the present tunnel outburst preventive rock plate thickness calculation method and the water-rich fault fracture zone mechanical model，such as incomplete factors and significant calculation error. Based on Janssen?s theory，parameters such as the horizontal angle between the tunnel axis and the fault fracture zone surface，the fault dip angle and the groundwater depth are introduced. The correction calculation formula for the outburst prevention rock plate thickness of the tunnel crossing the water-rich fault fracture zone is derived and verified by model test. On this basis，the influences of fracture zone distribution，fault fracture zone dip angle，water pressure and other factors on the rock plate thickness of tunnel are revealed. The results show that the calculation formula of the outburst prevention rock plate thickness has good applicability under the two conditions including fault fracture zone is inward/outward compared with rock plate for outburst prevention. Meanwhile，the thickness of tunnel outburst prevention rock plate increases with the increase of fault fracture zone distribution，water pressure，tunnel section and buried depth，and decreases with the increase of fault fracture zone inclination，the strength of ordinary surrounding rock and the intersection Angle between tunnel axis and fault fracture zone. The research results can provide theoretical reference for the anti-outburst safety calculation of similar tunnel engineering.

The weakly cemented Xiyu conglomerates are widely distributed in the northern and southern foothills of Tianshan Mountains in Xinjiang. The material composition of Xiyu conglomerates is complex，and their mechanical properties are poor. In order to scientifically understand the evolution laws of mechanical properties of weakly cemented Xiyu conglomerate，its grain fabric characteristics and macro mechanical properties were systematically studied by means of laboratory test and in-situ large-scale true triaxial test. The results indicate that：(1) The material composition of weakly cemented Xiyu conglomerate is relatively high in the three particle groups of crushed stones，coarse gravels，and medium gravels. And the particle size distribution of weakly cemented Xiyu conglomerate is poor. The inter-granular contact between large and coarse particles such as crushed stones and gravels involves either particle suspension or particle support. The inter-granular cementation is mainly pore-type cementation. (2) Due to the influence of particle arrangement，weakly cemented Xiyu conglomerates exhibit obvious anisotropic deformation characteristics. The deformation modulus is highest in the vertical direction，lowest in the direction of the particle's major axis(nearly perpendicular to the Tianshan Mountain)，and moderate in the direction of the particle's mid axis(nearly parallel to the Tianshan Mountain). However，with the increase of stress level，the weakly cemented Xiyu conglomerates tend to be isotropic. (3) Under triaxial stress state，weakly cemented Xiyu conglomerate shows strain hardening characteristics in the yield stage. After reaching peak strength，it shows typical plastic flow characteristics. (4) The shear strength of weakly cemented Xiyu conglomerates have obvious nonlinear characteristics，loading and unloading stress path effects and intermediate principal stress effects. The higher the stress level，the smaller the internal friction angle and the greater the cohesion. The internal friction angle of Xiyu conglomerate under unloading condition is higher than that under loading condition，while the cohesion under unloading condition is lower than that under loading condition. Under true triaxial loading，the peak strength increases with the increase of intermediate principal stress，and the effect of the intermediate principal stress on the shear strength parameter，cohesion，is more obvious. (5) The failure of weakly cemented Xiyu conglomerate under triaxial stress is mainly compression-shear failure. After failure，a steep main fracture zone is formed，and the main fracture zones are connected by tensile cracks. The test results provide an important basis for systematically understanding the macro mechanical properties and their evolution laws of the weakly cemented Xiyu conglomerates.

The“9•5”Luding earthquake triggered a large-scale co-seismic geo-hazard in the Hailuogou scenic area. Half of the scenic road sections were located within the range of seismic intensity IX(9 degrees)，resulting in severe damage to the roads and the complete loss of traffic capacity. To explore the geo-hazards development rules and post disaster reconstruction strategies of Hailuogou scenic road，multi-dimensional and stereoscopic methods were comprehensively employed，including remote sensing，LiDAR，unmanned aerial vehicle oblique photography，field survey，geological exploration，and the automatic extraction of structural planes. These approaches enabled a systematic investigation of the geo-hazards in the study area from the regional level to the local site. The results showed that：(1) there were 503 co-seismic geo-hazards developed in the study area，with a total area of 3.75×106 m2. These geo-hazards were primarily concentrated along the right side of section K10–K15，within an elevation range of 1 900 m to 2 900 m and a slope range of 30°to 60°. (2) The distribution rules of geo-hazards were mainly controlled by factors such as topography，lithology，epicenter，and river，and the spatial coupling with the main fault was not particularly strong. (3) The instability modes of geo-hazards could be divided into three types：high-level collapse，deposit landslide，and shallow slope surface collapse，which exhibited the characteristics of large quantity，linear distribution，and different scales. Among these，high-level collapse was mainly observed in hard rock areas such as granite and dolomite，while landslides and shallow collapses mainly appeared in soft rock areas such as schist and slate，and on the ice water accumulation slope of the Moxi Platform. (4) The deep canyon terrain and high seismic peak acceleration caused seismic amplification effects in the rupture zone of the hard rock slope，resulting in a large scale of high-level collapse. A hysteresis phenomenon was observed in the overall instability of thick deposit landslides under strong earthquake action. (5) In accordance with the geo-hazards development rules，the post disaster reconstruction project of roads in Hailuogou scenic area adopted the concept of disaster reduction and route selection，and adhered to the principle of avoiding major geo-hazard and treating minor geo-hazard. Four tunnels were constructed to avoid high-position collapses，and thirteen bridges were built to cross potential debris flow gullies. In conjunction with in-situ treatment measures such as grouting steel flower pipes and anchor rod frame beams，the disaster prevention and resistance ability of scenic roads was enhanced. The results systematically revealed the geo-hazards development rules of the Luding earthquake epicenter area. The proposed post disaster reconstruction strategies were comprehensively applied in engineering practice，providing important support for disaster identification and evaluation and post disaster road reconstruction work in strong earthquake areas.

In order to explore the influence of multi-stage cyclic loading with a constant amplitude on rock deformation，damage and permeability，a four-stage cyclic loading and unloading triaxial test was carried out on sandstone samples under different confining pressures. The permeability was measured and acoustic emission (AE) signals were monitored in real time during the test. The effects of confining pressure and cyclic loading on the characteristic stresses，permeability，b-value and RA-AF(risetime/amplitude - average frequency) value of AE signals during multi-stage cyclic loading are analyzed. The results show that：(1) Compared with the conventional triaxial compressive test，the volume strain of the sandstone crack under each stage of the multi-stage cyclic loading test is expanded，and the peak stress decreases. With the increase of confining pressure，the difference between the two peak stresses decreases. (2) Under the two loading conditions，the permeability decrease first and then increase. After cyclic loading，the permeability strain-based loss rate(PSL) of the rock sample is smaller，and the macroscopic deformation of the rock is aggravated. When the confining pressure increases，the PSL increases and the macroscopic deformation decreases. Under low confining pressure，the stress-based irrecoverable permeability coefficient(EIP) in each cycle is negative or small，and the permeability increases. Under high confining pressure，EIP value in the fourth cycle is positive，indicating that the permeability decreases，and the formation of seepage channel is affected by confining pressure constraints. (3) Furthermore，the b-value of AE signals under multi-stage cyclic loading fluctuates more than in the conventional triaxial test. Under the two loading modes，the rock samples are dominated by tensile cracks. Under the condition of multi-stage cyclic loading，there are more shear cracks in the rock sample，and with the increase of confining pressure，the proportion of rock tensile cracks gradually decreases，and the proportion of shear cracks increases.

In this research，triaxial shear tests under different stress levels and initial hydration damages were carried out on sandstone-grout composite specimens under different normal stresses and immersion times to investigate the shear mechanical properties of rock-grout composite structures. The results showed that the increased damage induced by hydration significantly reduced the shear resistances of the rock and the bonding surface, increased the deformation amount of the specimen and degraded its bearing capacity. The shear strength of the specimens decreased by 23.14%–35.46% under the condition of 30 d of immersion，while maintaining the same normal stress level. The increase of normal stress restricted the development of micro-fractures in the specimen and improved the bearing ability. The shear strength of the specimens increased by 97.15%–137.12% with increasing normal stress，while maintaining the same immersion time. The shear failure mode of the composite specimens is limited by the stress level and initial hydration damage. There were three typical failure modes, including shear slip along the rock-grout interface，mixed shear failure and partial rock failure. With increasing immersion time，the total strain energy，the elastic strain energy and the dissipated strain energy of the specimen decreased，and the energy required for specimen failure reduced. The dissipation ratio of the specimens decreased by 54.38%–57.56% with increasing normal stress at the same immersion time. The increase of normal stress raised the energy storage capacity in the specimen，as well as the input external energy required for fracture development，thus enhancing the bearing performance of the structure. According to the shear mechanical behaviors of the composite specimens，a shear model of soft rock-grout structures under different immersion times and normal stresses was established.

In order to investigate the asymmetric deformation characteristics and structural damage patterns in tunnel intersections，and to propose the reasonable type and suitable support system for the intersection under the extrusion deformation，the Yulong Snow Mountain Tunnel of Lijiang—Shangri—La Railway is selected as the engineering background in this paper，and based on the field monitoring，the investigation on the structural deformation and biased-pressure characteristics of the intersections sections is performed. On this foundation，the influence range of the intersection is analyzed through numerical simulation to investigate the influence of reasonable intersection type on the tunnel support effect. According to the results of the study，the intersection support structure，under the action of extruded surrounding rock，shows significant asymmetric deformation and biased-pressure characteristics. The support damage mostly occurs at the arch shoulder and arch waist. When a parallel guide tunnel intersects the main tunnel at 45°and is subsequently further excavated，stress concentration is observed on both the acute and obtuse sides of the main tunnel?s support，with the acute side experiencing higher stress levels and less deformation，indicating a severe structural biased pressure. The direction of structural biased pressure on the acute side of the main tunnel is related to the distance from the intersection，with a reversal in biased-pressure direction occurring between distances of 0.98D and 1.26D. Compared to 45°skewed intersections，h-shaped intersections prove more effective in distributing the main tunnel?s axial stress，circumferential stress，and deformation.

As an emerging hydraulic fracturing technology，cyclic injection has a promising application in glutenite reservoirs. Based on the true triaxial hydraulic fracturing system，the hydraulic fracturing experiments by continuous and cyclic injection are carried out under different stress conditions. By comparing the propagation characteristics，the propagation law of hydraulic fractures in glutenite under cyclic injection is clarified. The results show that the fracture propagation in glutenite is mainly controlled by two factors，including the stress difference and the structural characteristics，and the fracturing effect in glutenite can be improved significantly by cyclic injection. Under continuous injection，with the decrease of stress difference，the main controlling factor of fracture propagation will be changed from stress difference to gravel and natural fractures，and the glutenite will tend to produce scattered multiple fractures. There are limitations in enhancing the fracturing effect by pre-breakdown cyclic injection. Only under low stress difference(6 MPa)，the breakdown pressure of glutenite can be decreased by 19%. By applying cyclic load to the fracture surface，the non-uniform deformation of the glutenite will be promoted by post-breakdown cyclic injection，and the influence of glutenite structure on the fracture propagation will be strengthened，thus the formation of multi-branch fractures will be promoted as well. At the same time，the limit of in-situ stress conditions can be broken by post-breakdown cyclic injection，the multi-fracture propagation in glutenite can still be formed under the condition of high stress difference(10 MPa).

The presence of tension cracks at the rear edge of a slope can significantly impact the stability of rock slopes. Effectively predicting the precise location and depth of these tension cracks is crucial for conducting a reliable analysis of the stability of rock slopes that exhibit such features. A novel method has been developed for rock slopes lacking joints or featuring four or more joints，aiming to determine the location and depth of tension cracks at the rear edge of rock slopes by considering the underlying formation mechanism of these cracks. First，the nonlinear generalized Hoek-Brown(GHB) strength criterion is applied to incorporate the influence of joints into the calculation of rock mass strength. Then，focusing on the vertical development characteristics of tension cracks at the rear edge of the slope，the horizontal stress state of the rock mass at this location is identified as a crucial factor influencing the formation and progression of tension cracks. Thereby，a micro-wedge unit mechanical analysis model is proposed to obtain the horizontal stresses of the rock mass at the rear edge of slope. Finally，leveraging the top-down development pattern of vertical tension cracks at the rear edge of slope and the relationship between the ultimate stress level of these cracks and the tensile strength of the rock mass，a discriminant formula is formulated to determine the location and depth of tension cracks at the rear edge of the rock slope. The rationality and validity of the present method have been confirmed through comparisons with numerical simulation methods，laboratory test results，and engineering data. These research findings will establish a theoretical foundation for predicting the location and depth of tension cracks at the rear edge of rock slopes, thereby facilitating reliable stability analysis of rock slopes with tension cracks at the rear edge.

The traditional stability calculation theory and support structure design methods of deep buried tunnels are not suitable for the significant challenges posed by large deformations of soft rock under complex geological conditions. There is an urgent need for breakthroughs in this field. Firstly，the instability mechanism of squeezed large deformation tunnels and the interaction mechanism between surrounding rock and support structures are elucidated. Based on the elastoplastic theory，the stress at the elastic-plastic interface of the surrounding rock and the plastic zone radius of the rock are determined to establish the scope of stability analysis for the surrounding rock. Based on the energy method，the surrounding rock in the plastic zone and support structure are regarded as independent structures. The stress and deformation continuity conditions at the rock-support interface are introduced，and total energy equations for the stability analysis of the surrounding rock and the support structure are separately established. The stationary principle of potential energy and Rayleigh-Ritz method are used for analytical calculations to obtain the stability curve of the surrounding rock and the characteristic curve of the support structure. The rationality of the support structure is analyzed and evaluated by the graphic method. The influence of related parameters of the surrounding rock and the support structure and seismic forces on stability is investigated. The accuracy and practicality of the proposed method are verified through practical engineering applications. Finally，the frontier problems in further research are prospected. The results show that a deep buried tunnel convergence constraint design method based on structural stability theory is proposed，which conforms to NATM principles, modern tunnel engineering concepts and instability mechanism. This method achieves deformation control design. When the initial ground stress is 40 MPa，the contribution of the surrounding rock support is 91.4%，indicating that the surrounding rock is the main supporting force to maintain the stability of the tunnel. The elastic modulus of surrounding rock，internal friction angle, the strength of rock bolting，and seismic stress have significant effects on the stability of deep buried tunnels. Combined with the support structure design analysis of Muzhailing tunnel, the convergence constraint design method proposed is proved to have good engineering applicability. The research findings provide a new perspective for the design of support structures for deep buried tunnels.

The existence of faults in high-intensity earthquake areas has a serious impact on engineering structures and the longitudinal response of tunnels crossing faults needs to be studied further. The tangential foundation springs are used to analyze the tangential contact effect of surrounding rock-lining and axial deformation characteristics of tunnel，and an analytical solution for longitudinal response of tunnels crossing faults is presented. Firstly，the elastic foundation beam model is used to simulate the surrounding rock-tunnel structure interaction. Based on this，the differential equation for longitudinal response of tunnel structures is obtained. Wherein，the displacement of free field is applied on the distal end of normal foundation spring to simulate fault displacement. The analytical solution of the longitudinal tunnel response is gotten by using Green function. Secondly，the numerical solution from finite difference model of 3D is used to verify the validity of the proposed analytical solutions. The results show that the tangential contact effect of surrounding rock-lining has a significant impact on the longitudinal response of tunnel. Ignoring it，the peak bending moment error of structure reaches 35.33%. Finally，the effects of fault zone width，fault elastic modulus and lining concrete grade on the longitudinal response of tunnel are explored. As the fault zone width increases，the internal force of the tunnel structure decreases；increasing the lining concrete grade results in unfavorable effect on the structure；the increase in the elastic modulus of the surrounding rock in fault zone reduces the bending moment and shear force of structure，and increases the axial force，respectively. The research results can provide a theoretical basis for the anti-offset design of tunnels crossing faults.

Fouled ballast can commonly cause severe defects of ballasted trackbed including mud pumping and differential settlement，thus further endangering stable and safe operations of trains. To address this engineering challenge，ballast specimens with different fouling levels were prepared in the laboratory by adopting the classic fouling index(FI)，and subsequently subjected to monotonic triaxial compression tests. The newly-invented wireless，self-powered and smart sensors(SmartRock) were placed at different positions inside ballast specimens to measure real-time particle rotation data. The macroscopic shear strength behaviors of ballast specimens with different fouling levels were analyzed comparatively and linked to meso-scale ballast particle movement. The results show that increasing coal dust fouling level could cause gradual transition of macroscopic behavior from strain hardening to strain softening. When the fouling index(FI) value ranges from 10% to 15%，both peak deviator stress at failure and apparent cohesion reach their minimums，respectively. The rotation of ballast particles inside the triaxial specimens mainly occurrs in the vertical planes，whereas the vertical-plane rotations of ballast particles located closer to the bottom of clean ballast triaxial specimens increasingly attenuate due to the increasing restraint of lateral boundaries on particle movement. When the FI value reaches 15%，no discernible rotation pattern is observed for ballast particles inside triaxial specimens，which may be attributable to the loss of inter-particle force-transferring skeleton. When the FI value further exceeds beyond 15%，ballast particle rotations exhibite significantly increasing differences，probably resulting in macroscopic mechanical instability. The uniformity of ballast particle rotations determines macroscopic shear strength behavior to a certain extent and thus can be employed to estimate the actual fouling level of ballast beds. The findings are expected to provide theoretical basis and technical reference for Non-destructive evaluation of fouling degree，ballast-cleaning schedule optimization，and intelligent maintenance of ballasted trackbeds.

The primary consolidation of unconsolidated soft soil is not yet complete，so it is susceptible to producing excessive settlement，causing drag forces along the pile shaft installed in these soil layers. Few discussions on the bearing capacity of piles(i.e. negative frictional resistance) in underconsolidated soil have been reported，including the influence of the underconsolidation degree. In this paper，a parameter termed as initial consolidation degree， ，was defined to characterize the underconsolidation degree，and three model tests were carried out under different initial consolidation degrees，in which surcharge preloading was considered. The behavior of the negative frictional resistance of the pile under different initial consolidation degrees and surcharge levels was analyzed，and the coefficient of negative frictional resistance and neutral point depth were discussed. The results show that the initial consolidation degree has a significant effect on the negative frictional resistance of pile. With the increase of  (i.e.，the decrease of the underconsolidation degree of soil)，the settlement of pile，settlements of soil at different depths，axial force of pile shaft and negative friction resistance of pile all show a decreasing trend，and their behavior is basically similar under different loading levels. The average values of negative friction coefficient under  = 0.25，0.50 and 0.75 are 0.545，0.351 and 0.147，correspondingly. Compared to  = 0.25，the negative friction coefficients under  = 0.50 and 0.75 are reduced by 35.6 % and 73.0 %，respectively. The increase of  leads to the neutral point moving downward，but the downward rate gradually decreases. When  = 0.25，0.50 and 0.75，the neutral point depths are 0.53，0.75 and 0.76 of the pile depth，correspondingly. In addition，the increase of the surcharge level causes the increase of negative friction coefficient and the decrease of neutral point depth slightly，but the effect is not significant in the holistic view when the initial consolidation degree is identical. The research results can provide technical reference for the analysis and design of negative friction resistance of piles in unconsolidated soft soil.

To clarify the water-heat-salt migration and deformation characteristics of sulfate saline soil under rainfall，based on the climate characteristics and saline soil types of the Hexi region in Gansu Province，a geometric similarity ratio model(1∶6) of the natural site of sodium sulfate saline soil was made using the self-developed indoor baseplate-atmospheric dual-temperature control model box. Combined with the surface energy budget balance characteristics for the first time，this natural site model was used to study the multi-physical fields coupled changes within the sodium sulfate saline soil under no rainfall and rainfall. The results show that rainfall can lead to a decrease in reflected shortwave radiation，downward longwave radiation and surface temperature，an increase in surface net radiation and surface evaporation rate，and the increasing trend is related to rainfall. The rainfall leads to an increase in soil water content and conductivity，as well as a decrease in soil heat flux and temperature. Meanwhile，the rainfall leads to an increase in the heat release time of sulfate saline soil. In addition，the influence of rainfall on the water-heat-salt physical fields within the sulfate saline soil gradually weakens with increasing depth. During the transition of four seasons throughout the year，the sulfate saline soil undergoes a deformation process of first thawing settlement and then salt frost heave. Moreover，the thawing settlement and salt frost heave deformation of sulfate saline soil show varying degrees of increase under the influence of rainfall. The research results provide certain guidance for addressing environmental disasters and engineering issues in salted regions under the background of climate change.

Engineering geological problems，such as slope instability and cracking of roadbed fills，are closely related to the tensile strength of soil. The Brazilian splitting test was used to study the tensile strength properties of unsaturated compacted specimens and dehydrated specimen in this study. The objective was to study the evolution of the tensile strength in unsaturated compacted and dehydrated specimens across a broad range of the water content. Results show that with decreasing the water content，the tensile strength of compacted specimens initially increases and then decreases，reaching its maximum value at a critical moisture content. Conversely，the tensile strength of dehydrated specimens continues to rise and eventually approaches a stable level. The difference between these two types of specimens can be attributed to the fact that the tensile strength of compacted specimens is mainly affected by capillary suction stress generated at the bending liquid surface，whereas the tensile strength of dehydrated specimens is primarily influenced by factors such as capillary suction stress and cohesive forces. Then, microstructure images of both types of specimens obtained through electron microscopy scanning experiments were carefully analyzed and discussed. Finally，an unsaturated soil tensile strength model was established based on an effective stress formula that considers both capillary and adsorption effects. The effectiveness of this model was verified using measured data.